1. Field of the Invention
The purpose of this invention is to provide an aircraft pilot with an indication and warning of ground proximity via subconscious peripheral vision cues.
2. Description of the Prior Art
Over fifty percent of tactical aircraft fatalities occur due to impact with the ground during low altitude maneuvering. An United States Air Force study completed in 1984 showed that although low altitude flight accounted for only 10 percent of all tactical flight hours, 57 percent of the fatalities occurred in this regime. Considering night flights alone, the U.S. Navy lost 21 aircraft with 49 fatalities between 1986 and 1991 due to controlled flight into the ground or water. The term "controlled flight" indicates that the pilot literally flew the aircraft into the ground or water. Controlled flight into the ground during approach and departure account for the majority of all fatal spatial disorientation mishaps. Fatal spatial disorientation mishaps in all types of aviation (military, civil and commercial) have remained at a relatively constant 15 percent since accident statistics have been kept. These aircraft accidents continue to occur despite sophisticated ground proximity detection devices.
There are a number of systems used for ground proximity detection. Most consist of an altimeter that may be coupled with a vertical descent speed measuring device. The altimeters generally use reflected electromagnetic energy, as in a radar altimeter, to measure the distance Above Ground Level (AGL). The vertical descent rate input, when used, consists of measuring the rate of change in barometric pressure, or in sophisticated aircraft, inertial or radar measured descent rate. These become ground proximity warning devices when combined with a pilot selected threshold altitude and a visual and/or aural warning. When the aircraft descends below the selected threshold altitude, a warning is generated. There have been very few documented incidents of altimeter or ground proximity warning device failure. There have been many incidents of controlled flight into the ground with working ground proximity warning devices.
If the ground proximity warning devices are operating and set properly, there are three possibilities that account for controlled flight into the ground: (1) the pilot is consciously ignoring the warning; (2) the pilot is not consciously aware of the warning; or (3) there is insufficient time from warning to ground impact for the pilot to react. If we dismiss the first as a suicidal act, we are left with possibilities (2) and (3). This requires an examination of how the warning is imparted to the pilot.
Current ground proximity indicators present their warning via several methods or combinations of methods. These include: analog AGL altitude displays; digital AGL altitude displays; altitude warning tones; pre-recorded voice warning, e.g., "altitude" or "pull-up"; instrument panel warning lights; and visual warning symbols, e.g., a flashing "X" in the Head Up Display (HUD). It is possible for a pilot to be consciously unaware of an aural or visual warning. During periods of high stress and information overload, the human mind can fixate on one task and suppress or ignore information presented aurally or by the central vision. Low altitude flight, particularly during landing approach or low altitude maneuvering, generally requires high rates of information processing and is often stress inducing. To ensure the pilot is aware of the warning, the warning must surpass or override competing aural or visual sensory input. If the warning is not sufficiently compelling, the warning may be heard or seen but not perceived.
There are several U.S. Patents on ground proximity detection devices which function as described above. For Example, U.S. Pat. No. 5,187,478, by GROVE, discloses a descent rate warning system which alerts a pilot that there current descent rate may place the aircraft in danger. U.S. Pat. No. 5,220,322, by BATEMAN et al, discloses a proximity warning system which takes into consideration the degradation in performance of an aircraft near the ground. U.S. Pat. No. 5,038,141, by GROVE, discloses a ground proximity warning system which takes into consideration the flight configuration of the aircraft. U.S. Pat. 5,075,685, by VERMILION et al., discloses a altitude warning system having an audio warning when predetermined altitude parameters are exceeded. U.S. Pat. No. 5,134,394, by BEADLE, discloses a navigation apparatus which displays both altitude and attitude information in close proximity to each other. U.S. Pat. No. 4,936,142, by DAVIDSON, discloses a vertical speed indicator which may be used to accurately determine ground proximity.
Another concern with respect to preventing fatal spatial disorientation mishaps is the ability of the pilot to determine the current attitude, i.e., the orientation of the aircraft relative to a horizon, and to correct the attitude of the aircraft to prevent a controlled flight into the ground. Peripheral Vision Horizon Displays (PVHDs) were designed to assist in determining the attitude of an aircraft. These PVHDs were developed in the early 1980s and were limited to projection on the front instrument panel of the cockpit.
There are several examples of these PVHDs which are disclosed in U.S. Patents. For example, U.S. Pat. Nos. 4,616,226 and 4,743,903, both by MORLEY, disclose artificial horizon devices which illustrate aircraft attitude by projecting an artificial horizon on the instrument panel of the aircraft. The artificial horizon simulates aircraft pitch and roll by drawing the artificial horizon with respect to a vertical or horizontal line. The MORLEY device has the disadvantage of not being able to detect altitude, i.e., the height of the aircraft from the ground. U.S. Pat. No. 5,218,355, by BURKHARDT, discloses an artificial horizon device which also illustrates aircraft attitude by projecting an artificial horizon on an instrument panel of an aircraft. Finally, U.S. Pat. No. 5,072,218, by SPERO et al., discloses a HUD which provides attitude information to a pilot via a helmet.